The field of the disclosure relates generally to aircraft anti-icing systems, and more specifically to a system for electrically preventing the accumulation of ice build-up on leading edge surfaces.
Gas turbine engines typically include an inlet, a fan, low and high pressure compressors, a combustor, and at least one turbine. The compressors compress air which is channeled to the combustor where it is mixed with fuel. The mixture is then ignited for generating hot combustion gases. The combustion gases are channeled to the turbine(s) which extracts energy from the combustion gases for powering the compressor(s), as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Aircraft, during flight and/or while on the ground, may encounter atmospheric conditions that cause the formation of ice on airfoils and other surfaces of the aircraft structure, including wings, stabilizers, rudder, ailerons, engine inlets, propellers, rotors, fuselage and the like. Accumulating ice, if not removed, can add excessive weight to the aircraft and alter the airfoil configuration, causing undesirable and/or dangerous flying conditions. More specifically, if engines are operated within icing conditions at low power for extended periods of time, ice accumulation within the engine and over exposed engine structures may be significant. Over time, continued operation of the engine, a throttle burst from lower power operations to higher power operations, and/or vibrations due to either turbulence or asymmetry of ice accretion, may cause the accumulated ice build-up to be ingested by the high pressure compressor. Such a condition, known as an ice shed, may cause the compressor discharge temperature to be suddenly reduced. In response to the sudden decrease in compressor discharge temperature, the corrected core speed increases in the aft stages of the high pressure compressor. This sudden increase in aft stage corrected core speed may adversely impact compressor stall margin. In some cases, it may also lead to an engine flame out.
To facilitate preventing ice accumulation within the engine and over exposed surfaces adjacent the engine, at least some known engines include a de-icing system to reduce ice build-up on the gas turbine engine struts. Some known de-icing systems mechanically remove the ice with the use of pneumatic boots. In such a system, the leading edge zone or wing or strut component of an aircraft is covered with a plurality of expandable cuffs that are inflatable with a pressurized fluid, such as air. When inflated, the cuffs expand and crack accumulating ice which is then dispersed into the air stream. Although pneumatic boots have been used on commercial aircraft and some light twin or small jet aircraft, the system, which requires an air compressor and vacuum system, is expensive and adds appreciable weight to light aircraft. A similar mechanical system employs multiple juxtaposed electro-expulsive elements placed within an elastomeric or metal clad boot that is attachable to airfoil surfaces. When an electrical impulse is applied, the force effects an impulse separation of one element from the other that is sufficient to mechanically throw off thin accretions of ice. In each of these mechanical systems, boot operation affects the airfoil characteristics of the wing, with the result that the boots cannot be operated during landing or takeoff. In addition to the drawbacks of the added weight and expense of current mechanical ice removal systems, each of these systems requires visual attention to the degree of ice build-up and careful timing of activation for maximum effectiveness. Moreover, none of these systems are suitable for use as an anti-ice system (i.e. to prevent ice from forming).
Another common approach for de-icing and/or anti-icing aircraft surfaces involves the application of a chemical, such as for example alcohol, to reduce adhesion forces associated with ice accumulation and/or depress the freezing point of water collecting on the surfaces. Such systems may be used while the aircraft is on the ground or in flight. One such system prevents the build-up of ice on the leading edges of airfoil surfaces, including propeller and rotor blades, by the weeping of alcohol from a plurality of holes in an attached titanium cuff. Such an on-board chemical system may be costly to operate and rely on a finite supply of chemical during flight.
Some known anti-ice or de-ice systems include thermally removing ice or preventing the formation of ice. One known system diverts bleed air or hot air from one of the turbine stages to heat the airfoil leading edges. Other known thermal systems employ electrically conducting resistance heating elements, such as those contained in heating pads bonded to the leading edges of the aircraft or on the propeller or rotor blades, or those incorporated into the structural members of the aircraft. Heating pads of this type generally include an electrically conductive material in contact with wire or other metal heating elements dispersed throughout the conductive layer which is sandwiched between two layers of insulation. Electrical energy for the heating elements is derived from a generating source driven by one or more of the aircraft engines. The electrical energy is continuously supplied to provide heat sufficient to prevent the formation of ice or intermittently supplied to loosen accumulating ice. However, such systems are only usable where sufficient wattage is available to raise and/or maintain the temperature of the airfoil surface above the freezing point at typical aircraft speeds.
To achieve operational temperatures for such thermal systems, the power supply required to power a wire heating pad type anti-ice or de-ice system is significant, because of the inefficiencies of the resistive heating pad elements, and may not been a feasible alternative as anti-ice or de-ice systems for general aviation aircraft.